Facebook isn't afraid to make a splash, hence the decision back in February of this year to scoop up WhatsApp for $19 billion in cash and stock options. It remains Facebook's largest transaction to date, though it could prove a brilliant move in the long run, especially as WhatsApp keeps attracting more users. As of right now, WhatsApp is home to 500 million active users.

"Thanks to all of you, half a billion people around the world are now regular, active WhatsApp users. In the last few months, we've grown fastest in countries like Brazil, India, Mexico, and Russia, and our users are also sharing more than 700 million photos and 100 million videos every single day," WhatsApp co-founder Jan Koum stated in a blog post. "We could go on, but for now, it's more important that we get back to work -- because here at WhatsApp, we're just getting started."

At the time Facebook acquired WhatsApp, its purchase price broke down to $42 per user. Today it amounts to $38 per user and falling with each new person that signs up and becomes a regular user. Bear in mind that only includes what Koum considers "regular, active" users as opposed to the total number of people who are registered.

Now at half a billion strong, an argument could be made that WhatsApp was simply too big for Facebook to ignore, which itself is home to 1.23 billion monthly active users (as of December 2013). There remains a sizable disparity between the two, but in acquiring WhatsApp, Facebook ensures it will still be the biggest social playground for a long while to come.

It will also be interesting to see what kind of integration occurs over time. At its core, WhatsApp is a cross-platform mobile messaging app that dodges SMS fees. WhatsApp is free to download and use for the first year, and then just $0.99 per year thereafter.